Whether the parties made the land contract under a mutual mistake of existing fact that materially affected their agreed exchange.
Holding
Yes. Both sides mistakenly believed that the property was legally usable as income-producing residential rental property, and that mistake concerned a basic assumption underlying the contract.
Reasoning
A contractual mistake is a belief that does not accord with facts existing when the contract is made. The relevant question is not when the parties discovered the sewage problem, but whether the defect already existed at closing. The record supported the conclusion that it did: a prior owner had installed a nonconforming septic system, and the parcel's extremely limited size made a lawful replacement system impossible.
The mistake was mutual because both the Messerlys and the Pickleses believed the apartment building could be occupied and produce rental income. Condemnation showed that the building could not be used for any residential purpose, defeating the intended income-producing use and substantially altering the practical character of what the parties exchanged.
The Court rejected a rigid distinction between mistakes going to the "substance" of consideration and mistakes going merely to value. A single factual error may affect both the property's value and the essence of the bargain. Rather than treating Sherwood v. Walker and A & M Land Development Co. as establishing categorical rules, the Court adopted a case-specific approach: rescission may be appropriate when a mutual mistake concerns a basic contractual assumption and materially affects the parties' agreed performances.